Rotary bell cup atomizers are used to apply paint to workpieces, more particularly, they are used to paint automobile and other vehicle bodies. Known rotary atomizers include a rotating bell cup having a generally conical inner front flow surface extending between an inner, axially central opening and a radially outer atomizing edge. Conventional bell cup atomizers further include a deflector which is generally rotationally symmetric about a central axis and is positioned in front of the central opening such that paint entering the bell cup through the central opening impacts the rear surface of the deflector and is disbursed radially outwardly towards the front diverging flow surface of the cup, flowing thereover to the outer edge of the cup where it is atomized to a fine mist.
The paint so applied is known to follow a tortuous and turbulent path, from the nozzle at the cup center to the outer atomizing edge. Atomization is effected by centrifugal forces produced when the cup, mounted on a central motor shaft, is rotated at high speeds, typically at 60-70,000 RPM.
Bell cups can have different shapes and configurations. Air can be supplied around the outer periphery of the cup to form a shroud that is concentrically positioned over the bell cup, adjacent to where atomized coating material leaves the bell cup, to direct the atomized coating material in a controlled pattern toward the workpiece to be coated.
The bell shaped body can have a generally conical cavity defining an inner diverging flow surface at the front or distal end of the bell shaped body, the inner flow surface extending from an inner coating material source to a radially outer spray edge. In operation, the bell cup is rotated around a stationary nozzle, the nozzle having passageways or channels housed therein through which materials such as paint and cleaning solvent are supplied.
One known problem with bell cup atomizers is that coating material can accumulate on the outer exposed surfaces of the bell cup in use. During a subsequent use, the accumulated coating material can dislodge from the bell cup, be propelled into the paint stream, and undesirably mix with new coating material, especially after a paint change, and cause visible imperfections in the painted workpiece. These imperfections are called “dirt” in the industry parlance. Therefore, it is highly desirable to efficiently clean all outer surfaces of such unwanted material.
One solution is to separately feed solvent or jet air to the outer peripheral surfaces to remove or prevent the unwanted material from adhering thereto. See, for example U.S. Pat. Nos. 5,862,988, 5,707,009 and 5,106,025. Another solution, as disclosed for example in U.S. Pat. No. 5,707,009, uses a stationary nozzle having a plurality of channels that are separate from the coating material channel for delivering solvent to the inner flow surface and the outer surface of the bell cup. Since the solvent channels are independent from the coating material channel, the bell cup can be rinsed with solvent (rinsing or cleaning agent) without having to remove the paint from the paint channel. The feed nozzle, which is coaxially arranged with the bell cup, delivers either solvent or coating material on command from sources located upstream of the rear or proximal end of the bell cup.
In U.S. Pat. No. 5,707,009, the bell cup has an annular cavity located within the rear section of the bell cup, communicating with the solvent channels. The annular cavity creates a large annular space through which solvent flows and moves around the rearward edge onto the outer surface of the bell element ('009, col. 2, lines 3-20). During use, while the bell cup undergoes a painting operation, this annular cavity is prone to paint accumulation, forming undesirable “dirt” on a workpiece in subsequent applications. Improved cleaning of the outer periphery of the bell cup paint applicators is needed. The present invention addresses this need.
A more recent attempt to solve the “dirt” problem is disclosed in U.S. Pat. No. 6,050,499. Therein, a rotary cup atomizer is provided with solvent passages in the cup which communicate a paint reservoir with the outer peripheral surface of the bell cup. Solvent which flows out onto the outer peripheral surface of the bell cup through the passages is guided toward the marginal releasing edge of the bell cup. Assist air is spurted out through assist air outlet holes which are provided in the fore end face of a shaping air ring at positions radially on the inner side of shaping air outlet holes. At the time of a washing operation, the solvent which flows out onto the outer peripheral surface of the bell cup is forcibly pushed to the outer peripheral surface by the action of assist air and shaping air as the solvent is guided toward the fore end of the bell cup to wash away deposited paint therefrom.
In a typical coating operation, different flow configurations of coating materials can be required, thereby requiring changed flow-directing components. For some known bell cups, the entire bell cup atomizer must be detached from the supply manifold, and an entire new assembly must be attached, and this procedure must be repeated each time the coating operation requires a change in the flow configuration of the coating material, thereby resulting in the interruption of the paint cycle and unwanted downtime. Paint continuously discharging radially outwardly from the aforesaid deflector directly impacts the forward, radially inward diverging conical surface of the bell cup. This continuous impaction of coating material onto the inner flow surface of the cup can cause premature wear of this surface, thereby resulting in premature, but required, cup replacement, accompanied by its concomitant downtime, and an undesirable interruption in a production cycle. The invention disclosed herein alleviates this problem significantly and, in combination with one of its embodiments, presents an entirely new structural advance which provides precise rotational balancing of the high speed rotating cup about its axis, all thereby extending the life of the cup in its production cycles.